Intrauterine position has a large impact on the lives of Mongolian gerbils. Denote by 2M a gerbil that is positioned between 2 male fetuses, and by 2F a gerbil that is positioned between 2 female fetuses. For reasons that will become clear later, 2M males will be called Maxes and 2F males will be called Mins. The positions of fetuses and Mins and Maxes are illustrated in the figure below (which I stole and edited Principles of Animal Behavior):
In the uterus, Maxes essentially take the most testosterone (maximum), and Mins take the least (minimum). This has a big impact on who these gerbils will become as adults. Mins “have lower circulating levels of testosterone, less well-developed genital musculature, and lower reproductive success” than do Maxes (pdf). Mins end up spending more time caring for young gerbils and a lot less time having sex. In fact, Mins often end up caring for the offspring of the Maxes. It’s fascinating the impact of intrauterine position!
In general, I prefer the terms Max and Min over the usual alpha and omega. Hopefully this will become more clear in the next section.
Sensory Space Invaders
We all have seen human Maxes and Mins. I like to think of their behavior in terms of how much territory they routinely claim.
If a Max sits next to you on the train, he will spread his legs and take up a lot of space. A Min will slide over and make himself small. The Max behaves as if the space is his.
Maxes will invade all of your sensory space, whereas Mins will tend to only enter if invited.
Maxes are loud. They might stink up the air in a crowded room (from passing gas or being sweaty). They’ll put their hands on you. They might invade your sight by changing in front of you. When they drive, they’ll cut you off. Maxes are sensory space invaders.
Mins are quiet. They will only touch you if you’ve given them permission. They will go in another room to pass gas. In traffic, they will make space and let you in.
Robert Sapolsky noticed that when his Max baboons ate poison meat and died, the next generation changed its entire social structure, creating a more egalitarian and peaceful society.
It used to be thought that urbanization caused dominance or agression. Studies show that when when animals are put in confined spaces or are exposed to over crowded conditions, animals who were on the more dominant end of the behavioral spectrum, became even more dominant. Animals who were more submissive became even more submissive. Crowding and confinement conditions exaggerated behavioral traits, leading to Maxes and Mins of an extreme nature.
A dramatic study involving guppies demonstrate how environments can create Maxes. Min guppies have physical and behavioral differences. They are smaller and lack the color of Max. Their testis are sucked up in their body. Mins do not even have the capability to produce sperm. They do not act aggressive or territorial like their Max counterparts. Their biology is such that they are not space invaders. In fact, they try to disappear to ensure their safety. However, when Max is removed, within 35 minutes, Min’s testis descend, he grows in body size, develops color and stripes, and behaves in territorial ways that keep other fish biologically suppressed. New Max will swim to females and mate and keep other males away. Even if old Max is put back into the territory (as long as Min has gone through changes) he will continue to be max. Enviroment created New Max.
This was co-written by Charlene Lewis-Estornell
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